Wide-angle projection



April 21, 1931. w. G. WOLFE WIDE ANGLE PROJECTION Filed May 16, 1927 2 Sheets-Sheet l WOLFE April 21, 1931 N N y #7 a SINN W Q Aw .fiwmk Patented Apr. 21, 1931 UNITED STAT-ES PATENT OFFICE,

WALTER G. WOLFE, OF GREENWOOD, MASSACHUSETTS, ASSIGNOR TO WILMOT B. EVANS,

TRUSTEE, OF BOSTON, M'ASSACHUSETTS WIDE-ANGLE rnomc'rron Application filed May 16, 1927. Serial No. 191,589. a

In the projection of pictorial effects for observation, modern developments have introduced many difficulties. -As the moving .picture so-called represents amaximum of these difficulties I shall refer to'this art as one to which my invention is particularly applicable, although obviously capable of a wide range of usefulness. In such projection where photographic detail must be highly enlarged in order to be observable by an audience, it has been heretofore necessary to locate the projection apparatus at a distance from the screen in order to get sufficient magnification. This .has brought projecting apparatus back into or over the audience and in actual practice this arrangement has come to be recognized as a very serious menace to safety.

While back stage projection has been an ancient and obvious possibility, its practice under such conditions as are present with the moving picture industry-has been impossible.

In accordance with my invention I provide for back 'sta e projections so that the projector. may be ocated. away from the audien'ce and behind the plane of the fire cur-v tain. The desirabilit of such an arrangement is obviousl Asi e from the safet factor as regards reduction in fire risk an consequent. saving in insurance, it permits the .pictureto be shown in a lighted auditorium without any loss of strength or detail of the image on the screen, and without an distor tion, due to the fact that the beams rom the back stage projector "are horizontal, whereas those from the usual elevated projector at the back of the auditorium are angularly downward, iving the so-called key-stone distortive e ect which becomes more and more pronounced as the observer moves away from the center line of the theatre towards the "wings- Moreover, with the back stage projector, it ispossible to illuminate the stage while the motion picture is displayed, so'that actors may appear on the stage in full limelight during the run of the picture and the audience may observe both actors and picture simultaneously.

Where the projector is located in the back of the auditorium, it is necessary to enclose it in a booth which itself occupies much valuable seating space that might otherwise be used at each performance, thus resulting in a direct economic loss which is constant and continuing. 1 The whir of the motors isalso annoying to the audience and detracts from the desirability of the seats in proximity to theoperators booth. Moreover, the projector is often located a distance of 150 feet or more from the screen, thus:necessitating-higher powered lighting. units with increased factor of heat generation, whereas with my'back stage projector location the distance from the screen is from seventeen to twenty feet," with resultant economy in power consumption and reduction in fire risk, as well as eliminating the operators booth from the seating space of the theatre.

The possibilities in accordance with. my-invention will be dealt with in the following specification and are illustrated in the accompanying drawings. Throughout the s ecification and drawings like reference 0 aracters are employed to indicate corresponding parts, and in the drawings:

Fig. -1 is a lateral diagrammatic view of the problem.

Fig. 2 a face diagram view of theasame.

Fig. 3 is an illustrative diagrammatic treatment showin modification of lens surface.

Fig. 4 is a ia ammatic view ofan optical system in accor ance with my invention.

Fig. 5 an exaggerated view of a portion of the curv surface of-a modified lensin accordance with my invention, and I Fig. 6 is a schematic illustration of an arrangement in accordancewith my invention.

In considering a problem of the class herev in involvedin which wide angle projection is to be attained, Ihave, .as heretofore sug-f 9 gested, selected pictorial pro ection as best adapted for the purposes'of isclosures. As

the projection of moving ictur'es so-call ed involved a rather. extreme egree-of magn1fi-' cation as well as other immediateand serious problems, I will discuss my inventon particularly in connection with that art inasmuch as it involves certain novel phases of the com bination. In fact, it may be convenient to approach the general problem through this The advantages of such a desired arrangement have been obvious from the start. The projection of stereopticon or-magic lantern pictures on a translucent screen was common practice in times past, but the extreme magnification called for in modern pictorial projection as illustrated by the moving picture indust ofi'ered what seemed to be insurmounta le difliculties. Wide angle projection lenses for detail such as pictorial or photographic minutiae have generally been considered as impossible optics from the practical point of view. This was due to the extreme spherical aberrations involved, as well as to chromatic difficulties. Optical science has, of course, known how to correct for aberration and how to correct for color.

Nevertheless, to the best of my knowledge and belief this knowledge has not been deemed applicable to produce practical results as reguired in this art. This is due to the difculties in conditions and requirements be-' tween large lenses such as astronomical mir rors and relatively smaller optics such as the projection art requires. Furthermore, in the projection art there is the extreme'difiicultyof definiteness in correction sufiicient to malntain detail without disturbing continuity of pictorial effect.

In Figs. 1 and 2 I have attempted to indicate diagrammatically the problem as it existed. In Fig. 1 L is an ordinary diverging lens, S the screen and C the curvature of the sphere concentric with the effective curvature of the lens L. As is well known the distortion as illustrated by this figure is due to the dearture of the spherical surface of curvature g} from the plane surface of the screen ,8. This gives what I have shown in Fig. 2 as a pin cushion effect P; The opposite or barrel efiect is indicated by the circle B. In this case the square defined by the line X is what might be considered as the normal pictorial field defined on the screen by the aperture. In

correctiinv for such difliculties we may consider the illustration of Fig. 3. In this a lens A has for example a central spheric surface as indicated between the lines R. Beyond that surface is a modified surface or annular ortion indicated by (2. Such an annular surace has been generally known in optics, but generally in connection with large mirrors where an aspheric surface is produced by working dawn the margins of a spheric, I

mention this because while such a general surface has been known and while it has what might be called a theoretical application to my present invention, it is not a practical surface utilizable as such and my invention consists in part in a modification of this surface to' get those results which make a new and revolutionary combination of projector screen and even theatre itself possible.

At this point attention is invited to the diagram shown in Fig. 5. This may be considered as the line of curvature from the center outwardly, OO indicating the optical axis; In this we may consider the portion between this axis and the radius R as a spheric and the elements 2 of the broken line extended beyond as indicating the plurality of surfaces each more divergent from the curvature of the sphere and each preferably of an increasin length as indicating a zone of greater widt Instead, therefore, of the continuous curvature a ofthe lens margin outside of the spherical portion my lens has what may be considered as a plurality of definite annular surfaces constituting as a whole the general trend of the surface as indicated at a in Fi 3 different therefrom from the fact that t ey are definite independent optical surfaces of perfectly definite values. It is only possible to treat these surfaces diagrammatically because they are very narrow surfaces and their v ry narrowness is a factor which will be realy understood by those skilled in the art from the following.

The treatment of light by optics involving definite annuli necessarily results in the projection of differentiated rings on the intercept, as for example, on the screen S. By making these optical annuli, however,

sufliciently narrow so that the rings on the intercept are of awidth vwithin the intercept of distinct vision, I findit possible to use these definite surfaces 2 to eliminate s heri-' cal aberration to an extent that it is ignorable and without in the slightest disturbing the interpretive value of pictorial effects distributed zonally.

Referring to the problem in its practical present application, we may consider the. .grea indicated by thebracket Y in Fig. 6

as that occupied by the audience. F may in. dicate the ordinary stage front, P the proscenium arch,S the screen and D the ordinary ,fi e proof curtain. We may consider M as a moving picture machine and LL asyany lens system in accordance with'my invention. In this arrangement it will be noted' that the bracketed distance between the screen S and the back wall W is a relatively short distance as indicated at G. This distance ranges, I

believe," from about twenty feet which repre sentsa rather deepvbacksta e, to something less than twenty feet in shal ower stages, the

average distance as I observedi-t being about fifteen feet. This back stage :distance may its Ill

. invention are undoubtedly applicable to a vantage at longer distances, as well as'shorter, suchas store window picture display. 1 am discussing it particularly with reference to this back stage distance because it constitutes an immediate and definite problem. In

notice the screen is always set back from five to ten feet from the proscenium arch, in order for front seat observation.

The advantages attained by the combination indicated in Fig. 6 are so obvious as hardl to need mention. I heretofore stated that the desirability of moving the projection apparatus and especially the film from the audience or from the proximity of normal exit and even from the sight of the audience in case of fire, has been written large in the tra edies of fire reports. The possibility of ropping an asbestos curtain as deep as the proscenium arch is obvious. There are, however, other advantages one of which I mention as very important. The long distance projection necessitated by the increase in size of the so-called movie house has necessitated a tremendous increase in power at the light source. With every increase of candle power the fire hazard is increased. Back stage projection requires only a portion of such illumination and herein lies the solution of many practical difficulties.

Returning once more to the matter of optics involved, it will be seen that the successive surfaces 2 produce in general that hyperbolic tendency heretofore attained by the very delicate correction of aspherical lens. My lenses ma therefore be considered generally as asp erics but the methematical definiteness of the successive annuli must be borne in mind. I do not mean by this that the annuli need to be maintained in true planes nor that they intersect each other sharply. I mean they must be of progressive divergence considered as planes and preferably of increasing width but of a sufficient narrowness to give on the picture a zonal width within the limits distinct vision.

I have endeavored in Fig. 4 to show a practical system as empl%yed by me in moving picture projection. have indicated at 1 a standard pro'ector lens which is about three inch focus. uch a lens unmodified projects a picture about twenty-one feet uare at a distance of seventy feet. With t is I combine a system consisting of a crown member 2. which I preferably form as a double concave lens the rear face having a central surface Z surrounded by a series of annular surfaces 2 as described in connection with Fig. 5. The flint member 3 as shown is a lano-convex. The second systemK2 3 is used in practice to secure thedesired corrected divergence and can be made to give a standardized size of picture of approxlmately twenty-one feet square at a distance of only seventeen feet. It ma be noted by comparison that with the or inary projecting'lens at such a distance a picture of only five feet square could be attained.

My invention is, of course, capable of all the variations of optical design common to lens production and. is not confined to the plano-concave system. In fact, it may be produced in meniscus form ver satisfactorily. All such are ca able of a l the chromatic corrections by t e relative figuring ofthe flint member 3 and the crown member 2. My invention may be practiced with any translucent screen and my combination of projector and lens system, screen and theatre may be made to suit any varieties of architecture or settin arrangement.

What I there ore claim and desir tose cure by Letters Patent is 1. In combination in a projection uip 9o ment for backstage or like projection o abnormal wide angle on a relativel large screen, a projector having a long istance optical s stem but placed at a fractional distance o the normal front focus of its 95 system from said screen, and a relatively larger negative lens of wide aperture inclusive of a concave side having a centralspherical surface and amarginal aspheric surface progressively increasing in focal length to- 1 ward the edge of the lens and spaced from' the positive system to receive the normal projected beam therefrom and spread it without substantial change of the back focus of the projector. 1

2. In a rojection e'qui ment for backstage or li e projection o abnormal wide angle on a relatively large screen, a projector havin a long distanceoptical s stem but place at a fractional distance of t e normal front focus of its system from said screen, and a relatively larger negative lens of wide aperture inclusive of a concave side having a central spherical surface and a marginal aspheric surface progressively increasing in focal length toward the edge of the lens outwardly and disposed to receive the beam from the projector and spread it on the screen without substantial change of the back focus of the projector.

3. In a projection equi ment for backstage or li e projection o abnormal wide angle on a relatively large screen, a projector havin a long distance optical system but lace at a fractional distance of the normal, 125

ront focus of its system from said screen. and a relatively larger negative lens of wide aperture having concave surfaces of central sphericitybut of marginally aspheric tendency progressively outwardly and spaced at from the positive system to receive the normal projected beam and spread it without substantial disturbance of the back focus of the projector.

4. In combination with a positive optical projecting system of high magnification but low beam divergence, of a relatively larger negative lens of wide aperture and wide angle for projection on a flat display screen disposed at a distance from the projecting system abnormally short for its normal functions, said negative lens being inclusive of a concave side havlng a central spherlcal surface, and a marginal aspheric surface progressively increasing in focal length toward the edge of the lens whereby the distortion of the intercept of the wide angle spread of the beam is prevented.

5. In combination with a positive optical projecting system of high magnification but 'relatively low beam divergence, of a relatively larger negative lens of wide aperture and Wide angle for projection on a translucent flat display screen disposed at a distance from the projecting system abnormally short for its normal functlons, said negative lens being inclusive of a concave side having a central spherical surface and a marginal aspheric surface progressively increasin in focal length toward the edge of the ens whereby the distortion of the intercept of the wide angle spread of the beam is prevented. 0

In testimony whereof I aflix my signature.

WALTER G. WOLFE. 

